The invention relates to a guide vane element for a gas turbine that extends between an inner and an outer platform, and that can be connected in a fixed manner with other adjoining guide vane elements.
Guide vanes from stators of gas turbines consist of high-alloy metal and are often manufactured, as described, for example, in U.S. Pat. No. 4,015,910, as individual guide vane elements which are then connected with each other to form a guide vane ring. In most cases, such an individual element comprises at least one vane blade, as well as an outer and an inner platform attached to the vane blade. If such elements are connected with each other to form an entire guide vane unit, the respective outer and inner platforms form the cover bands that extend cylindrically and delimit the area through which the operating gases flow. The manufacture by elements facilitates and simplifies the production process. In particular, number, size, and complexity of the casting molds are reduced.
As described, for example, in EP 0 949 404 A1, the elements can be less susceptible to breaks caused by thermal and mechanical loads during operation in their combined form, and also can be easily replaced. The individual elements are also much easier to finish, which is particularly advantageous for the drilling of cooling channels, as they are required for film cooling.
The problems with such guide vane elements usually occur in the connection zones between the platforms. The elements or their platforms should be joined tightly and fixed to each other so that a tight unit of guide vanes is created and a cover band is formed that prevents the uncontrolled exchange of the operating gases and cooling gases separated from the cover band. However, the connection and its geometry must not be so rigid and limiting that the mechanical and thermal loads occurring as a result of the temperature differences between the hot operating gases and cold cooling gases during operation result in material fatigue or even breaking of the elements.
EP 0 903 467 A2 describes, for example, pairs of guide vane blades that can be interconnected with flanges, in which the connection is designed so that the meshing prevents a thermal load and the associated breaks of the elements during operation while simultaneously preserving the tightness of the cover bands.
The invention provides guide vane elements that can be connected with each other to form guide vane blades, groups, or even a mechanically fixed ring of guide vanes. The connection between the guide vane elements is tight even at the temperatures occurring during operation, without experiencing undesirably high stresses under the mechanical and thermal loads. According to an embodiment of the invention, a first guide vane element for a gas turbine includes a vane blade extending between a platform that is located radially inward in relation to the main housing of the gas turbine, and a radially outward platform. A flange is provided on at least one edge of the platform adjoining an adjacent second guide vane element in the circumferential direction in relation to the main axis, and on the side of the platform facing away from the vane blade. The second guide vane element can be attached to the first guide vane element by a second flange provided on the second guide vane element. The second flange is provided on a second platform connected to the second guide vane element. The guide vane elements are connected by their respective platforms, with the connected platforms forming a substantially cylindrical cover band.
The connection between two adjoining platforms includes in an area facing away from the vane blade a portion that is in flush contact with the adjoining flange. An expansion gap remains between the adjoining platforms in the area facing the vane blade and the high temperature operating gases.
According to aspects of the invention, when the guide vane elements are in a cold state, a gap remains at the connection of the two elements in the area that will face the hot operating gases, while a tight and flush connection exists in the cooler area exposed to the cooling gases. If such a connection is exposed to typical operating temperature conditions, the platforms exposed to the hot operating gases are able to expand with the heat, while the material in the areas containing the actual connection hardly expands at all. This prevents the build-up of stresses in the connection areas as a result of the differences in material behavior. The above-described features prevent a thermally caused gap that would limit the tightness of the connection, and also clearly reduces thermal stresses in the connection areas. This means that this surprisingly simple method is able to prevent thermal stresses and loose points in the connection areas.
A preferred embodiment of the present invention includes features that prevent an exchange of air flowing between the side of the platform facing the vane blade or the side of the cover band, and the side of the cover band facing away from the vane blade. These features ensure an improved tightness of the platforms, and can include sealing lips, sealing lamellas, sealing tubes, and seals that extend into a gap on the vane blade side of the platforms. The use of such features that preferably extend across the entire length of the edge between adjacent platforms increases the tightness of the created cover band, in general, and even if the final operating temperature conditions that correspond to an equilibrium state have not yet been reached or are no longer present in the elements.
According to aspects of an embodiment of the invention, rings can be arranged in the area of the attachment means, with the rings projecting in the direction of the second guide vane element beyond the edge, and with a flush connection with the second guide vane element being achieved via the rings. It is particularly preferred that these rings are constructed as projections cut out of the flange used to connect adjoining platforms, and in particular in the area of an expansion of the flange that is intended for the attachment means. Such rings can be cut in a simple finishing step into elements having different forms and shapes, for example simple rings around attachment holes in the flanges, but also bands or areas extending across the entire length of the edge on the side exposed to the cooling gases.
The rings can also be formed by separate washers that are inserted in the attachment area between two elements. Possible attachment methods for all embodiments can include, but are not limited to screw-nut connections, rivet connection, and welded or hard-soldered connections.
According to the invention, another embodiment can include the above-described features on the outer and inner platforms and furthermore, on both sides of the platforms for connections with additional guide vane elements that adjoin on either side of the platforms. In this manner, the advantages described above, including the prevention of stress build-up, and the maintaining of a tight connection can be achieved for all connection points. The individual elements to be connected need not be identical. The adjoining guide vane elements may be elements with different vane blades or, instead of vane blades, also may be channels. Any desired number of elements can be connected with each other.